This study aimed to determine the effects of kefir addition on dry matter (DM), organic matter (OM) and protein apparent digestibility, faecal characteristics, haematology, and biochemistry parameters of healthy dogs. Twenty-one adult Golden Retriever dogs were divided into three groups: Control (CON, no kefir), KF1 (2 × 106 CFU/g kefir), and KF2 (4 × 106 CFU/g kefir). The dogs were fed for a 30-day administration period. Blood was taken from all dogs on the initial (day 0) and last day (day 30). Stool consistency of the dogs were scored according to 1–5 system (1 = diarrhea-like, 5 = formed and too dry) on the last five days before taking fresh faecal samples to determine digestibility, short-chain fatty acids (SCFA), ammonia, pH and DM levels. The highest DM, OM and protein digestibility levels were determined in KF2 (p < 0.05). Kefir addition improved the faecal scores of KF1 and KF2 (p < 0.05). Faecal pH was lower in KF2 than CON (p < 0.001). The lowest faecal ammonia levels were found in KF1 and KF2 (p < 0.001). Increased faecal acetic and total SCFA levels were detected in the kefir groups, and KF2 had the highest propionic acid level (p < 0.05). The lowest cholesterol level was determined in KF2, and the lowest triglyceride levels were determined in KF1 and KF2 on the 30th day (p < 0.05). A significant decrease in cholesterol, triglyceride, and creatinine was detected to the KF2 dog’s first and last day (p < 0.05). Blood MCHC was affected by kefir in KF2 (p < 0.05). These results indicated that 2–4 gr of kefir had positive effects on nutrient digestibility, colon fermentation, stool consistency, and the blood parameters of dogs.Highlights Kefir is a traditional dairy product with multiple probiotic characteristics that boosts the immunity and overall gastrointestinal health of animals. In a study involving 21 dogs, dietary supplementation of kefir improved protein digestibility of food and reduced serum cholesterol and triglyceride levels. Kefir reduced faecal ammonia and increased SCFAs. Kefir could be further developed as a functional dietary food supplement to improve the quality of life of dogs.